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Characteristics of the
Major Elements as
Fertilizer
Japhet C. Paypa
University of southeastern Philippines –Mabini Campus

The form of N applied in inorganic form will be either as the
ammonium cation (NH4+) or the nitrate anion (NO3-), or
the combination of both (NH4NO3), ions that have
completely different behaviors in soil.

Urea [CO(NH2) 2], which contains neither
ammonium nor nitrate, will be quickly
hydrolyzed when brought into contact with a
soil, the hydrolyzed N form being ammonium.
Urea left on the soil surface will hydrolyze
with the production of gaseous ammonia (NH3)
that will be released into the atmosphere,
resulting in a significant loss of applied N.

The NH4+ cation will participate in the
cation exchange phenomenon of the soil, and
that in the soil solution will undergo
nitrification into the NO3– anion.
The NH4+ cation moves in the soil
solution primarily by diffusion

• Gaseous ammonia can be used directly as a fertilizer. It has a
pungent odour and is toxic to plants and humans when
concentrated but harmless in dilute form.
• When liquefied under pressure for transportation, it is referred to
as liquid or anhydrous ammonia (containing 82 percent N).
Anhydrous ammonia

Characteristics of the Major Elements as Fertilizer

Aqua ammonia
• Aqueous ammonia is a solution containing
water and ammonia in any proportion, usually
qualified by a reference to ammonia vapour
pressure.
• Commercial grades commonly contain 20–25
percent N.

Ammonium Sulphate
• AS is the oldest synthetic N fertilizer.
• It contains about 21 percent N (all as
ammonium) and 23–24 percent S (all as
sulphate).
• It is an acid-forming fertilizer and is highly
soluble in water.

• AN is produced by neutralizing nitric acid with ammonia.
• Fertilizer-grade AN has 33–34.5 percent N, of which 50 percent is
present as ammonium and 50 percent as nitrate.
• It is usually in a granular or prilled form and coated with a
suitable material to prevent absorption of moisture and caking in
storage.
• It is a valuable N fertilizer, but also a dangerous explosive, hence,
its trade and use as fertilizer is forbidden in many countries.
Ammonium Nitrate

Calcium ammonium nitrate
• CAN is a mixture of AN and finely pulverized
limestone or dolomite, granulated together.
• It contains 21–26 percent N, half in the form of
ammonium and the rest in the form of nitrate.
• Its use does not make the soil acid by virtue of
the carbonate in it.

• Also known as Chilean nitrate of
soda or Chile saltpetre, it was the
first mineral N fertilizer to be used.
• It is obtained by refining the crude
nitrate deposits called Caliche
found in Chile.
• It contains about 16 percent N, all
as nitrate.
Sodium Nitrate

• Urea is the most important and widely used N fertilizer
in the world today.
• It is a white, crystalline, non-protein, organic N
compound made synthetically from ammonia and CO2.
• Urea contains 46 percent N, all in amide (NH2) form
and it is readily water soluble.
• It is the most concentrated solid N fertilizer that is
produced as prills or granules of varying size
Urea

phosphorusThe form of P applied as fertilizer may be as the
orthophosphate anion (PO43–), the diphosphate anion
(H2PO4–), or the monophosphate anion (HPO42–), depending
on the fertilizer chemical composition.

Even though a highly soluble form of P is applied,
such as phosphoric acid (H3PO4), the orthophosphate
anion (PO43–) will quickly interact with the soil,
forming precipitates with the elements Ca, Fe, and Al,
and that remaining in soluble form will exist in the
soil solution as either the diphosphate anion (H2PO4
–) or as the monophosphate anion (HPO42–),
depending on the pH of the soil, and moves
primarily in the soil solution by diffusion.

• Single superphosphate (SSP) is the oldest commercially produced
synthetic fertilizer and the most common among the group of
superphosphates.
• The prefix “super” probably refers to its superiority over crushed
animal bones when it was first produced in the 1840s.
• SSP is a mixture of monocalcium phosphate [Ca(H2PO4)2] and
calcium sulphate or gypsum (CaSO4.2H2O).
• It contains 16 percent water-soluble P2O5, 12 percent S in
sulphate form and 21 percent Ca.
Superphosphates

Basic slag• Basic slag is a by-product of the steel industry.
• It is considered to be a double silicate and phosphate of
lime [(CaO)5P2O5SiO2].
• It contains 10–18 percent P2O5 (part of which is citrate
soluble), 35 percent CaO, 2–10 percent MgO and 10 percent
Fe.
• Basic slag can be used as a fertilizer-cum-soil conditioner
because it contains lime and citric-acid-soluble P.

• PR can also be used directly as a fertilizer. It
contains 15–35 percent P2O5.
• The quality of PR as a fertilizer depends on its
age, particle size, degree of substitution in the
crystal structure and solubility in acids.
Phosphate rock (PR)

Partially acidulated phosphate rock (PAPR)
• PAPR is obtained by the partial acidulation of PR to
convert only a part of its P into water-soluble form, as
compared with complete acidulation, where fertilizers
such as SSP or TSP are produced.

• A slow-acting product used as a component of
multinutrient fertilizers but it is rarely used as a
fertilizer by itself in present times
Dicalcium phosphate (CaHPO4)

Potassium• The K form in fertilizer is as the potassium cation (K+),
and when in solution participates in the cation exchange
phenomenon of the soil.
• The K+ cation moves in the soil primarily by mass flow.

Potassium chloride (MOP)• Potassium chloride (KCl), also called muriate of potash
(MOP), is the most common K fertilizer.
• It is readily soluble in water and is an effective and cheap
source of K for most agricultural crops.
• Grades of MOP vary from 40 to 60 percent K2O.
• Fertilizer containing 60 percent K2O is almost pure KCl
containing about 48 percent Cl.

• SOP is actually a two-nutrient fertilizer
containing 50 percent K2O and 18 percent S,
both in readily plant available form.
• It is costlier than MOP but is particularly
suitable for crops that are sensitive to chloride
in place of KCl.
Potassium sulphate (SOP)

The Ca form applied as a liming material or as a fertilizer is
as the calcium cation (Ca2+), and when in solution
participates in the cation exchange phenomenon of the soil.
The Ca2+ cation moves in the soil primarily by mass flow.

• contains 50–68 percent Ca (Ca × 1.4 = CaO);
CaLCIUM OXIDE

slaked lime [Ca(OH)2]• contains 43–50 percent Ca

agricultural limestone (CaCO3)• contains 43–50 percent Ca

dolomite (CaCO3.MgCO3)• contains 24–32 percent Ca

• CAN: contains 7–14 percent Ca;
• calcium nitrate [Ca(NO3)2]: contains 20 percent Ca;
• calcium chloride (CaCl2.6H2O): 15–18 percent Ca;
• SSP: contains 18–21 percent Ca;
• gypsum (CaSO4.2H2O): contains 23 percent Ca;
• calcium chelates: variabl
others

MagnesiumThe Mg form applied as a liming material or as a fertilizer is
as the magnesium cation (Mg2+), and when in solution
participates in the cation exchange phenomenon of the soil.
The Mg2+ cation moves in the soil solution primarily by
diffusion.

magnesium oxide (MgO)• contains 42 percent Mg (Mg × 1.66 = MgO);

magnesite• contains 24–27 percent Mg

dolomitic limestone (MgSO4.CaSO4)
• contains 3–12 percent Mg

• magnesium sulphate anhydrous (MgSO4): contains 20
percent Mg;
• magnesium sulphate monohydrate (MgSO4.H2O): contains 16
percent Mg;
• magnesium sulphate heptahydrate (MgSO4.7H2O): contains
10 percent Mg;
• magnesium chloride (MgCl2.6H2O): contains 12 percent Mg;
• potassium magnesium sulphate (K2SO4.2MgSO4): contains 11
percent M
others

The S form in fertilizers is as the sulfate anion (SO4 2–), and
when in solution interacts with other elements, mainly Ca
and Al (existing as cations in the soil solution), to form
precipitates.
The SO4 2– anion moves in the soil solution primarily by
diffusion.

ammonium sulphate (NH4)2 SO4• contains 24 percent S

ammonium sulphate nitrate• contains 12 percent S

potassium sulphate• contains 12 percent S; s

potassium magnesium sulphate• contains 22 percent S

magnesium sulphate monohydrate• contains 22 percent S

• magnesium sulphate heptahydrate (MgSO4.7H2O): contains 13 percent
S;
• gypsum/phosphogypsum (CaSO4.2H2O): contains 13–17 percent S;
• elemental S products: contain 85–100 percent S; sulphur bentonite:
contains 90 percent S;
• pyrites (FeS2): contains 18–22 percent S;
• sulphate salt of micronutrients: contain variable amounts of S.
others

Fertilizers containing nitrogen
and phosphorus

Mono-ammonium phosphate (MAP)
MAP (NH4H2PO4) is
produced by reacting
phosphoric acid with
ammonia. It contains 11
percent N and 55 percent
P2O5. It can be used
directly as an NP fertilizer
for soil application or as a
constituent of bulk blends.

Mono-ammonium phosphate (MAP)
DAP [(NH4)2HPO4] is an
important finished fertilizer
as well as an intermediate
in the production of
complex fertilizers and bulk
blends. It is produced by
treating ammonia with
phosphoric acid. It typically
contains 18 percent N + 46
percent P2O.

Ammonium nitrate phosphate
ANP is produced by reacting PR
with nitric acid. Several grades
are produced and a typical grade
contains 20 percent N and 20
percent P2O5. Also known as
nitric phosphates or
nitrophosphates, all of them
contain 50 percent of the total N
in nitrate form and 50 percent as
ammonium

Ammonium phosphate sulphate
These are in reality three-
nutrient fertilizers containing N,
P and S, all in watersoluble, plant
available forms. APS can be
seen as a complex of AS and
ammonium phosphate. Both the
common grades (16–20–0) and
20–20–0) also contain 15
percent S, which comes from the
AS portion.

Urea ammonium phosphates (UAPs)
UAPs are produced by reacting
ammonia with phosphoric acid
to which urea is also added in
order to increase the N content
in the product. The most
common example of this type of
NP complex is 28–28–0 (the first
UAP to be commercially
produced in the world).

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Characteristics of the Major Elements as Fertilizer

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Characteristics of the Major Elements as Fertilizer